1. Field of the Invention
This invention pertains to radio antennas, particularly to microwave antennas, and most particularly to microstrip (or "patch") microwave antennas.
2. Reference
Microstrip Antennas, D. M. Pozar, Proceedings of the IEEE, Vol. 80 No. 1, January, 1992, page 79 et seq (hereinafter, "Pozar").
3. Description of the Related Art
The physical size of an antenna is proportional to the wavelength of the signal it is intended to transmit or receive. As higher frequencies, with their shorter wavelengths, have been exploited, smaller antennas have become possible. The exploitation of frequencies in the GHz. range has led to the development and use of the microstrip antenna, which Pozar describes as "a metallic patch printed on a thin, grounded dielectric substrate" (Pozar at page 79). Such antennas can be inexpensive and compact.
Such inexpensive and compact antennas, in turn, have led to a broadening of the field of devices in which radio communication is used, such as employee badges that transmit the employee's identity or electronic shelf labels that receive and display price information dynamically. Since such devices might be required in large quantities, it is desirable that each unit be inexpensive; since such devices must operate portably or remotely, it is desirable that they consume little power.
Prior-art devices incorporating microstrip antennas employ conventional means for connecting the antennas to receiving or transmitting apparatus; the present invention provides a detector integrated into the microstrip antenna, enabling video, if, af, or dc signal to be obtained directly from the patch. This enhances compactness and lowers the cost and power consumption.